Imaging lens

ABSTRACT

Disclosed herein is an imaging lens, including: a first lens having positive (+) power and being biconvex; a second lens having negative (−) power and being concave toward an image side; a third lens having positive (+) power and being biconvex; a fourth lens having positive (+) power and being convex toward the image side; and a fifth lens havign negative (−) power and being concave toward the image side, wherein the first lens, the second lens, the third lens, the fourth lens, and the fifth lens are sequentially disposed from an object side.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of Korean Patent Application No.10-2011-0108128, filed on Oct. 21, 2011, entitled “Imaging Lens”, whichis hereby incorporated by reference in its entirety into thisapplication.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an imaging lens.

2. Description of the Related Art

Recently, due to the advancement in technology, mobile terminals such asmobile phones and personal digital assistants (PDAs) are currently usedfor not only making simple phone calls but to also perform functions formulti-convergence such as playing music or movies, watching TV, andplaying games. One of the leading factors for such multi-convergence isa camera module.

In general, a compact camera module (CCM) has a compact size and isapplied to portable mobile communication devices such as camera phones,PDAs, and smartphones and various information technology (IT) devicessuch as toy cameras.

In regard to lenses mounted in conventional camera modules, a four-lensstructure is used to realize a high pixel resolution. However, as thepixel size is reduced, it is difficult for the lenses to correspondinglyimplement the performance thereof.

SUMMARY OF THE INVENTION

The present invention has been made in an effort to provide an imaginglens having excellent optical characteristics.

According to a first preferred embodiment of the present invention,there is provided an imaging lens, including: a first lens havingpositive (+) power and being biconvex; a second lens having negative (−)power and being concave toward an image side; a third lens havingpositive (+) power and being biconvex; a fourth lens having positive (+)power and being convex toward the image side; and a fifth lens havingnegative (−) power and being concave toward the image side, wherein thefirst lens, the second lens, the third lens, the fourth lens, and thefifth lens are sequentially disposed from an object side.

The second lens, the fourth lens, and the fifth lens may be formed tohave a meniscus shape.

A distance TTL from an incident surface of the first lens on the objectside to the image side and a total focal length F of the imaging lensmay satisfy the following conditional expression:

1.1<TTL/F<1.35.

A curvature radius of the first lens on the object side may be set to begreater than a curvature radius of the first lens on the image side.

A curvature radius of the second lens on the object side may be set tobe greater than a curvature radius of the second lens on the image side.

A curvature radius of the third lens on the object side may be set to begreater than a curvature radius of the third lens on the image side.

A curvature radius of the fourth lens on the object side may be set tobe greater than a curvature radius of the fourth lens on the image side.

The fifth lens may be formed such that a sweep angle (SWEEP ANGLE) ofthe fifth lens at an end of an effective diameter of the fifth lens onthe image side is equal to or less than 46°.

An inflection point may be formed on each internal surface of the fifthlens on the object side and the image side.

The first lens, the second lens, the third lens, the fourth lens, andthe fifth lens may each be formed to be aspherical.

The imaging lens may further include a stop, wherein the stop isdisposed closer to the object side or the image side than the firstlens.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram illustrating an imaging lens according toan embodiment of the present invention;

FIG. 2 is a graph showing astigmatic field curves of the imaging lensaccording to an embodiment of the present invention;

FIG. 3 is a graph showing distortion of the imaging lens according to anembodiment of the present invention; and

FIG. 4 is a graph showing coma aberration of the imaging lens accordingto an embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various features and advantages of the present invention will becomeapparent from the following description of embodiments with reference tothe accompanying drawings.

The terms and words used in the present specification and claims shouldnot be interpreted as being limited to typical meanings or dictionarydefinitions, but should be interpreted as having meanings and conceptsrelevant to the technical scope of the present invention based on therule according to which an inventor can appropriately define the conceptof the term to describe most appropriately the best method he or sheknows for carrying out the invention.

The above and other objects, features and advantages of the presentinvention will be more clearly understood from the following detaileddescription taken in conjunction with the accompanying drawings. In thespecification, in adding reference numerals to components throughout thedrawings, it is to be noted that like reference numerals designate likecomponents even though components are shown in different drawings. Termsused in the specification, ‘first’, ‘second’, etc. can be used todescribe various components, but the components are not to be construedas being limited to the terms. The terms are only used to differentiateone component from other components. Further, in describing the presentinvention, a detailed description of related known functions orconfigurations will be omitted so as not to obscure the subject of thepresent invention. Further, when it is determined that the detaileddescription of the known art related to the present invention mayobscure the gist of the present invention, the detailed description willbe omitted.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram illustrating an imaging lens 100according to an embodiment of the present invention.

Referring to FIG. 1, the imaging lens 100 includes, a first lens 110, asecond lens 120, a third lens 130, a fourth lens 140, and a fifth lens150 sequentially disposed from an object side. Also, the imaging lens100 may further include a stop 105 that is disposed closer to the objectside or an image side than the first lens 110.

First, to obtain an image of an object (subject), light corresponding toimage information of the object sequentially passes through the firstlens 110, the stop 105, the second lens 120, the third lens 130, thefourth lens 140, the fifth lens 150, and a filter 160 to be incident ona light receiving device 170.

Here, the first lens 110 has positive (+) power and is biconvex.

Also, the second lens 120 has negative (−) power and a meniscus shapethat is concave toward the image side.

In addition, the third lens 130 has positive (+) power and is biconvex.Accordingly, the imaging lens 100 may achieve a high resolution and aslim size.

Also, the fourth lens 140 has positive (+) power and a meniscus shapethat is convex toward the image side.

In addition, the fifth lens 150 has negative (−) power and a meniscusshape that is convex toward the image side.

Here, the fifth lens 150 is formed to have an inflection point on eachinternal surface on the object side and the image side so that a chiefray angle (CRA) of the fifth lens 150 and a CRA of an image sensor,which is a light receiving device, may be matched. Accordingly, ratio ofmarginal illumination may be improved, and a decrease in productivity ofthe imaging lens 100 may be prevented.

Meanwhile, the first lens 110 may be formed of a material having a greatAbbe number and the second lens 120 may be formed of a material having asmall Abbe number, thereby reducing chromatic aberration.

Also, the third lens 130 is formed to have smaller power than the firstlens 110.

In addition, the first lens 110, the second lens 120, the third lens130, the fourth lens 140, and the fifth lens 150 are formed to beaspherical.

Also, the stop 105 is disposed closer to the object side or the imageside than the first lens 110, and selectively converges incident lightto adjust a focal length.

Meanwhile, the imaging lens 100 according to the embodiment of thepresent invention may have a focal length F of, for example, 2.8 mm orless and a field of view (FOV) of 60° or greater. However, the focallength F and FOV of the imaging lens 100 according to the presentembodiment of the present invention is not limited thereto.

Also, the filter 160 may be formed of an infrared ray blocking filter(IR cut filter), but the type of the filter 160 according to the presentembodiment of the present invention is not limited thereto.

The infrared ray blocking filter blocks radiation heat emitted fromexternal light so that the radiation heat is not transferred to thelight receiving device 170.

That is, the infrared ray blocking filter transmits visible rays butreflects infrared rays to be emitted to the outside.

Also, the light receiving device 170 having a surface on which an imageis formed may be formed of an image sensor that converts an opticalsignal corresponding to a subject image, to an electrical signal. Theimage sensor may be, for example, a charged coupled device (CCD) or acomplementary metal oxide semiconductor (CMOS), but is not limitedthereto.

The imaging lens 100 according to the embodiment of the presentinvention has optical characteristics as shown in Table 1 below.

TABLE 1 Lens Curvature surface radius Thickness Refractive Abbe Lensnumber (mm) (mm) index number shape Remarks S1 infinite 0 — — Flat StopS2 1.800552 0.555385 1.544 56 Asphere L1 S3 −36.771 −0.0272 Asphere S44.03686 0.247717 1.632 23.4 Asphere L2 S5 1.680682 0.594997 Asphere S69.024377 0.110811 1.544 56 Asphere L3 S7 −15.3803 −0.06502 Asphere S8−2.02202 −0.49456 1.544 56 Asphere L4 S9 −0.89994 −1.11119 Asphere S1014.46622 6.91E−02 1.544 56 Asphere L5 S11 1.096596 9.12E−01 Asphere S12infinite 1.517 64.2 Flat Filter S13 infinite Flat S14 infinite — — —Flat Image sensor

As shown in Table 1, all surfaces of the first lens 110 (L1), the secondlens 120 (L2), the third lens 130 (L3), the fourth lens 140 (L4), andthe fifth lens 150 (L5) of the imaging lens 100 are aspherical.

Also, values denoted by “−” in Table 1 are undefined values.

Also, S1 denotes a surface that determines a light amount of the imaginglens 100 according to the embodiment of the present invention, and Stopmarked in the remarks column of S1 denotes the stop 105 (S1) which isused to adjust the light amount.

Here, the stop 105 is disposed closer to the object side than the firstlens 110, but the position of the stop 105 according to the embodimentof the present invention is not limited thereto and may also be disposedcloser to the image side than the first lens 110.

Table 2 below shows aspheric constants of aspherical lenses of theimaging lens 100 according to an embodiment of the present invention.

TABLE 2 K A B C D E S2 0 −0.01413 −0.00778 −0.02006 0.000785 0.0024 S3 0−0.10971 0.337872 −0.58682 0.45104 −0.09954 S4 0 −0.22546 0.614614−0.88307 0.628083 −0.13339 S5 0 −0.21613 0.435828 −0.45746 0.207889−0.00481 S6 0 −0.15862 0.071111 −0.03314 0.095271 −0.04795 S7 0 −0.120570.020052 −0.02296 0.018017 0.014146 S8 −3.66663 −0.08874 0.07554−0.05193 −0.00164 0.00944 S9 −3.39503 −0.11595 0.129208 −0.067810.020968 −0.0026 S10 0 −0.02978 −0.01115 0.007724 −0.00134 0.000077 S11−6.79738 −0.05291 0.013976 −0.00368 0.000539 −0.00003

As shown in Tables 1 and 2, S1 denotes the stop 105 which is used toadjust a light amount. The stop 105 has no aspheric constant because itis flat.

Also, S11 and S12 denote the filter 160, and S13 denotes the imagesensor which is the light receiving device 170 and has no asphericconstant because it is flat.

In addition, an aspheric constant regarding the imaging lens 100according to the embodiment of the present invention may be calculatedaccording to Equation 1 below.

$\begin{matrix}{{Z(h)} = {\frac{{ch}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}h^{2}}}} + {A\; h^{4}} + {B\; h^{6}} + {C\; h^{8}} + {D\; h^{10}} + {E\; h^{12}}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Z: distance from a vertex of a lens in an optical axis direction

c: basic curvature of a lens

h: distance from a vertex of a lens in a direction perpendicular to theoptical axis

K: Conic Constant

A, B, C, D, E: Aspheric Constant

A total focal length F of the imaging lens 100 according to theembodiment of the present invention and focal lengths F1, F2, F3, F4,and F5 of the first lens 110, the second lens 120, the third lens 130,the fourth lens 140, and the fifth lens 150 are as shown in Table 3below.

TABLE 3 Item Total focal length F of imaging lens 3.87E+00 Focal lengthof the first lens (F1) 3.155091 Focal length of the second lens (F2)−4.74182 Focal length of the third lens (F3) 10.47052 Focal length ofthe fourth lens (F4) 2.549882 Focal length of the fifth lens (F5) 4.9916TTL 4.8 Sweep angle 37

A distance TTL from an incident surface of the first lens 110 on theobject side to the image side and the total focal length F of theimaging lens 100 may satisfy the following conditional expression.

1.1<TTL/F<1.35  (1)

The conditional expression (1) is a relational expression about arelationship between the distance TTL and power of the imaging lens 100according to the embodiment of the present invention. If the imaginglens 100 is designed to have a value greater than the conditionalexpression (1), productivity of the imaging lens 100 may decrease, andif the imaging lens 100 is designed to have a value smaller than theconditional expression (1), it is difficult to provide opticalperformance of the imaging lens 100.

Accordingly, by satisfying the conditional expression (1), the imaginglens 100 may be manufactured with high productivity and it may be easyto provide optical performance of the imaging lens 100.

Also, a curvature radius rdy s2 of the first lens 110 on the object sideand a curvature radius rdy s3 of the first lens 110 on the image sideaccording to the embodiment of the present invention may satisfy thefollowing conditional expression.

rdys3<rdys2  (2)

The conditional expression (2) is related to characteristics of thecurvature radius of the first lens 110 according to the embodiment ofthe present invention; by setting the curvature radius of the first lens110 on the object side to be greater than the curvature radius of thefirst lens 110 on the image side, shape tolerance may be reduced.

Also, a curvature radius rdy s4 of the second lens 120 on the objectside and a curvature radius rdy s5 of the second lens 120 on the imageside according to the embodiment of the present invention may satisfythe following conditional expression.

rdys5<rdys4  (3)

The conditional expression (3) is related to characteristics of thecurvature radius of the second lens 120 according to the embodiment ofthe present invention; by setting the curvature radius of the secondlens 120 on the object side to be greater than the curvature radius ofthe second lens 120 on the image side, sensitivity of the second lens120 may be reduced, but at the same time, the lenses having a bettershape may be formed during injection molding.

Also, a curvature radius rdy s6 of the third lens 130 on the object sideand a curvature radius rdy s7 of the third lens 130 on the image sideaccording to the embodiment of the present invention may satisfy thefollowing conditional expression.

rdys7<rdys6  (4)

The conditional expression (4) is related to characteristics of thecurvature radius of the third lens 130 according to the embodiment ofthe present invention; by setting the curvature radius of the third lens130 on the object side to be greater than the curvature radius of thethird lens 130 on the image side, the overall sensitivity of the thirdlens 130 may be reduced, but at the same time, an inflection point oneach surface of the third lens 130 may be minimized.

Also, a curvature radius rdy s8 of the fourth lens 140 on the objectside and a curvature radius rdy s9 of the fourth lens 140 on the imageside according to the embodiment of the present invention may satisfythe following conditional expression.

rdys9<rdys8  (5)

The conditional expression (5) is related to characteristics of thecurvature radius of the fourth lens 140 according to the embodiment ofthe present invention. The curvature radius of the fourth lens 140 onthe object side is set to be greater than the curvature radius of thefourth lens 140 on the image side. When the curvature radius of thefourth lens 140 on the object side is set to be smaller than that of thefourth lens 140 on the image side, the distance TTL from the incidentsurface of the first lens on the object side to the image side is notreduced, thereby deteriorating aberration characteristics.

Accordingly, by satisfying the conditional expression (5), the distanceTTL from the incident surface of the first lens on the object side tothe image side may be reduced, and aberration characteristics may beimproved.

In addition, a sweep angle L5 S11 A at an end of an effective diameterof the fifth lens 150 on the image side may satisfy the followingconditional expression.

L5S11A<46°  (6)

The conditional expression (6) represents a condition under which totalinternal reflection of the fifth lens 150 is minimized.

Here, a sweep angle refers to an angle between the object side and theimage side, which is measured from an end of the fifth lens 150 on theimage side.

If the sweep angle L5 S11 A is greater than 46°, strong internalreflection is generated when capturing an image due to reflection of thefifth lens 150 on the image side and total reflection of the fifth lens150 on the object side, and this causes deterioration of image quality.

Accordingly, by satisfying the conditional expression (6), generation ofinternal reflection may be reduced when capturing an image, therebypreventing deterioration of image quality.

FIG. 2 is a graph showing astigmatic field curves of the imaging lens100 according to an embodiment of the present invention. FIG. 3 is agraph showing distortion of the imaging lens 100 according to anembodiment of the present invention. FIG. 4 is a graph showing comaaberration of the imaging lens 100 according to an embodiment of thepresent invention.

As illustrated in FIG. 2, the graph of astigmatic field curves showsaberration characteristics of a directional component X of light on thex-axis and a directional component Y of light on the y-axis according toan image height (ANGLE) seen from the object side, which is a verticalaxis, and a focus position (FOCUS), which is a horizontal axis. Here, ascan be seen from the graph of FIG. 2, X and Y are adjacent to eachother, and thus, images do not diffuse and resolving power thereof isnot deteriorated.

Also, as shown in FIG. 3, the graph shows distortion shown on ahorizontal axis according to an image height (ANGLE) seen from theobject side. Here, as can be seen from distortion that is mainly between1.5 and 1.7 on the horizontal axis, there is substantially littledistortion.

In addition, as shown in FIG. 4, the graph of the coma aberration showstangential and sagittal aberration characteristics according towavelengths according to an image height. Here, it can be seen that aswavelengths are adjacent to a horizontal axis, there is little yellowaberration.

According to the preferred embodiments of the present invention, animaging lens having excellent optical characteristics may bemanufactured so as to obtain high resolution and a slim size of theimaging lens, and also, chromatic aberrations may be improved.

Although the embodiments of the present invention has been disclosed forillustrative purposes, it will be appreciated that the imaging lensaccording to the invention is not limited thereto, and those skilled inthe art will appreciate that various modifications, additions andsubstitutions are possible, without departing from the scope and spiritof the invention.

Also, all simple modifications and changes will be construed as beingincluded in the present invention, and the specific scope of theinvention is defined by the appended claims.

What is claimed is:
 1. An imaging lens, comprising: a first lens havingpositive (+) power and being biconvex; a second lens having negative (−)power and being concave toward an image side; a third lens havingpositive (+) power and being biconvex; a fourth lens having positive (+)power and being convex toward the image side; and a fifth lens havingnegative (−) power and being concave toward the image side, wherein thefirst lens, the second lens, the third lens, the fourth lens, and thefifth lens are sequentially disposed from an object side.
 2. The imaginglens as set forth in claim 1, wherein the second lens, the fourth lens,and the fifth lens are formed to have a meniscus shape.
 3. The imaginglens as set forth in claim 1, wherein a distance TTL from an incidentsurface of the first lens on the object side to the image side and atotal focal length F of the imaging lens satisfy the followingconditional expression:1.1<TTL/F<1.35.
 4. The imaging lens as set forth in claim 1, wherein acurvature radius of the first lens on the object side is set to begreater than a curvature radius of the first lens on the image side. 5.The imaging lens as set forth in claim 1, wherein a curvature radius ofthe second lens on the object side is set to be greater than a curvatureradius of the second lens on the image side.
 6. The imaging lens as setforth in claim 1, wherein a curvature radius of the third lens on theobject side is set to be greater than a curvature radius of the thirdlens on the image side.
 7. The imaging lens as set forth in claim 1,wherein a curvature radius of the fourth lens on the object side is setto be greater than a curvature radius of the fourth lens on the imageside.
 8. The imaging lens as set forth in claim 1, wherein the fifthlens is formed such that a sweep angle (SWEEP ANGLE) of the fifth lensmeasured at an end of an effective diameter of the fifth lens on theimage side is equal to or less than 46°.
 9. The imaging lens as setforth in claim 1, wherein an inflection point is formed on each internalsurface of the fifth lens on the object side and the image side.
 10. Theimaging lens as set forth in claim 1, wherein the first lens, the secondlens, the third lens, the fourth lens, and the fifth lens are eachformed to be aspherical.
 11. The imaging lens as set forth in claim 1,further comprising a stop, wherein the stop is disposed closer to theobject side or the image side than the first lens.